1. Field of the Invention
The present invention relates to an air intake duct as a passageway for supplying the air to an engine, and a method for manufacturing such an air intake duct, and particularly relates to an air intake duct in which noise is reduced at the time of air intake and a method for manufacturing such an air intake duct. The present invention also relates to a method for welding resin molded pieces with each other by use of a hot plate, and particularly relates to a hot plate welding method for welding molded pieces which are made of different kinds of resins different in melting point, by use of a hot plate.
The present application is based on Japanese Patent Applications No. 2000-144930, 2000-156420, and 2000-217330, which are incorporated herein by reference.
2. Description of the Related Art
In an air intake system of a motorcar engine, there is a problem that noise is generated in an air cleaner hose, an air intake duct, or the like, at the time of air intake. Such an air intake noise is harsh on the ears particularly at the time of a low engine speed. Conventionally, therefore, a side branch 101 and/or a resonator 102 are provided in an air intake duct 100 so as to reduce noise of a specific frequency calculated on the basis the Helmholtz resonance theory or the like, as shown in FIG. 17.
However, the side branch 101 may reach about 30 cm in length at the longest, and the resonator 102 may reach 14 liters in volume at the largest. Thus, there is a problem that such a noise absorbing apparatus occupies a large space in an engine room so as to reduce the degree of freedom in mounting other parts.
Therefore, Unexamined Japanese Utility Model Publication No. Sho. 64-22866 discloses that an orifice is disposed in an air intake duct and an air intake passageway is narrowed in the position of the orifice so as to reduce air intake noise. By narrowing the air intake passage way in such a manner, the acoustic mass increases so that the air intake noise in a bass range can be reduced.
In addition, Unexamined Japanese Utility Model Publication No. Hei. 3-43576 discloses an air intake noise reducing apparatus comprising two air intake ducts connected in parallel in an air cleaner case, branch ducts branching from the two air intake ducts respectively, a common resonator to which the respective branch ducts are connected, and an on-off valve provided on the upstream side of a connection portion of a branch duct in one of the air intake ducts, the on-off valve being opened selectively in accordance with the running condition of an engine.
According to the apparatus disposed in the aforementioned 3-43576, the on-off valve is controlled to change over the number of air intake ducts between one and two in accordance with the engine speed. Thus, the intake air quantity can be controlled in accordance with the engine speed, and the air intake noise can be reduced.
However, in the aforementioned method in which the air intake passageway is narrowed, there is a problem that the intake air quantity is insufficient at a high engine speed so that the output is lowered.
In addition, in the apparatus disclosed in the aforementioned 3-43576, an electronic control circuit, an electromagnetic on-off valve, a diaphragm actuator, or the like, is used to drive the on-off valve. That is not desirable from the point of view of the cost. In addition, because the electronic control circuit, the electromagnetic on-off valve, or the like, is required, the apparatus becomes so complicated that it is not only expensive but also considerable in the number of man-hour for maintenance.
Therefore, Unexamined Japanese Patent Publication No. Hei. 11-343938 discloses an air intake duct formed of non-woven fabric containing thermoplastic resin fibers by thermal compression molding. By forming an air intake duct out of a non-woven molded body in such a manner, it is possible to reduce the air intake noise effectively. In addition, in the same publication, there is a statement that the following three can be considered as the reason why the air intake noise is reduced, and it is considered that the air intake noise is reduced by the synergistic effect of the three reasons.
(1) Since the non-woven fabric is an elastic body, the non-woven fabric has a vibration damping operation, and sound waves are restrained from being generated by vibrations of duct walls.
(2) Energy of sound waves entering a large number of gaps among the fibers of the non-woven fabric is weakened by the operation of the viscosity and heat conduction of the gaps, and the fibers themselves resonate with the fluctuation of sound pressure so that the sound energy is attenuated.
(3) At least a part of the duct walls have some degree of permeability. Since a part of the sound waves pass such duct walls, stationary waves are restrained from being generated.
There is, however, a problem that the non-woven fabric molded body is so expensive, in comparison with general resin molded bodies, that the air intake duct formed of the non-woven fabric molded body becomes much more expensive than conventional air intake ducts.
By the way, resin molded articles are used in various fields because they have properties that they do not corrode or rot as metal or wood does, and they are inexpensive and light in weight. In addition, most of resin molded articles are formed of thermoplastic resin in order to save global resources by recycling. Then, various molding methods such as compression molding, transfer molding, injection molding, extrusion molding, blow molding, and so on, are used. With the advance of molding machines and mold structures, resin molded articles having complicated shapes have been able to be molded easily.
However, there is a case that it is still difficult to manufacture a molded article having a complicated shape by molding at a time. In addition, it is often necessary to form parts of a molded article out of different kinds of resins. In such a case, a plurality of molded pieces are molded respectively, and thereafter integrated by welding.
Welding resin molded pieces is performed as follows. That is, joint surfaces of a pair of molded pieces to be welded are heated. The molded pieces are brought into pressure contact in the condition that at least one of the joint surfaces is melted. In that state, both the molded pieces are cooled. As the method of heating the joint surfaces, there are known a method using a heated hot plate; a method in which a pair of molded pieces are subjected to vibration in the condition that they are brought into pressure contact with each other, so that they are heated by frictional heat; and so on. The former is called a hot plate welding method, and the latter is called a vibration welding method. Further, a method for vibrating molded pieces by use of ultrasonic vibration is called an ultrasonic welding.
Of such welding methods, the hot plate welding method is carried out as follows. In this method, joint surfaces of a pair of molded pieces to be welded with each other are brought into contact with the surfaces of a hot plate heated to a temperature not lower than softening points of the molded pieces so that the molded pieces are melted. After the hot plate is removed, the joint surfaces of the pair of molded pieces are brought into pressure contact with each other, and cooled in that condition. Since the hot plate welding method is simple in equipment and easy in welding, it is used broadly especially.
However, when molded pieces formed of resins different in melting point are welded with each other by use of the hot plate welding method, there may arise a failure. For example, to weld two molded pieces having a large difference in melting point from each other, it is necessary to heat the hot plate to a temperature not lower than the melting point of the higher-melting molded piece. If both the molded pieces are brought into contact with such a hot plate, the lower-melting molded piece may be melted in a portion other than the joint portion thereof, or softened and deformed even if it is not melted.
Even if there is a small difference in melting point, there may arise a failure. For example, when non-woven fabric made of low-melting thermoplastic resin fibers is welded with an opening portion of a cylindrical molded piece made of high-melting thermoplastic resin without damaging the air permeability of the non-woven fabric, ex. in the manufacturing method of the aforementioned air intake duct, it is desired to do as follows. That is, the non-woven fabric is prevented from melting while the circumferential edge portion of the opening portion of the molded article is melted. In this condition, the non-woven fabric is impregnated with the molten resin so as to be welded therewith. In this case, if the non-woven fabric is not heated to some extent, the molten resin is cooled so that the impregnation becomes insufficient to cause a failure in joint. However, if heating is performed by the conventional hot plate welding method, there is a problem that the non-woven fabric is also melted so that the air permeability is damaged.
To solve such a problem, for example, it is necessary to perform welding as shown in FIG. 18. In FIG. 18, hot plates A and B are formed to sandwich a thermal insulating plate 400 therebetween so that the hot plate B will be higher in temperature than the hot plate A. Then, a molded piece 200 made of low-melting resin is brought into contact with the hot plate A while a molded piece 300 made of high-melting resin is brought into contact with the hot plate B. Thus, the heating temperatures of the hot plates A and B are selected suitably so that the aforementioned problem can be prevented.
However, in the aforementioned method, two hot plates are required. Alternatively, the surface temperatures can be indeed set by one hot plate respectively, but the hot plate increases in size. Further, to control the surface temperatures of the hot plate, it is necessary to provide sensors and temperature regulators for the respective surfaces. Thus, there is a problem that the welder becomes large in size, the cost increases, and there is a severe restriction from the point of view of the space where the welder is installed.
The present invention was developed in consideration of such circumstances. It is an object of the present invention to dispose a porous member such as non-woven fabric most suitably to thereby not only suppress air intake noise but also reduce the usage of the non-woven fabric so as to make an air intake duct inexpensive.
It is another object of the present invention to reduce the loss in intake pressure in an air intake duct. It is still another object of the present invention to manufacture such an air intake duct stably while the porous member is thermally welded to the opening of the duct body uniformly so as to enhance the welding strength.
Further, it is still another object of the present invention to provide a method in which resin molded pieces different in melting point can be welded with each other by one hot plate at low cost without making a welder larger in size.
It is still another object of the present invention to provide a method in which non-woven fabric made of thermoplastic resin fibers is welded with a molded piece having a higher melting point than the non-woven fabric at low cost without damaging the air permeability of the non-woven fabric.
According to the first aspect of the present invention, there is provided a method for an air intake duct to be disposed between an outside air intake port of a motor car and an intake manifold of an engine, comprising: a duct wall having an opening formed in a predetermined portion of the duct wall, the opening being long in a longitudinal direction of the duct wall, a whole of the opening being covered with a porous member, the opening having a lateral width which is not shorter than {fraction (1/20)} of circumferential length of the duct wall.
A longitudinal position of the opening is preferably set to overlap with an antinode of a generated resonant wave. A longitudinal center of the opening is preferably located in a position of xc2xc of whole length of the duct wall from an end portion of the duct wall. The longitudinal center of the opening is preferably located in a position of xc2xc of whole length of the duct wall from an end portion of the duct wall in opposition to the outside air intake port.
According to the second aspect of the present invention, there is provided an air intake duct comprising: a duct body constituted by a large cylindrical portion made of resin and a small cylindrical portion projecting outward from a part of a duct wall of the large cylindrical portion, the small cylindrical portion having an opening formed at a head of the small cylindrical portion to thereby make the inside of the large cylindrical portion communicate with the outside of the large cylindrical portion; and a porous member covering a head of the opening of the small cylindrical portion.
According to the third aspect of the present invention, there is provided a method for manufacturing an air intake duct, comprising: forming a duct body constituted by a large cylindrical portion made of resin and a small cylindrical portion projecting outward from a part of a duct wall of the large cylindrical portion, the small cylindrical portion having an opening at a head of the small cylindrical portion to thereby make the inside of the large cylindrical portion communicate with the outside of the large cylindrical portion; and thermally welding a porous member containing a thermoplastic material with the small cylindrical portion so as to cover the opening.
Preferably, the small cylindrical portion optionally has a flange portion formed at a head of the opening, a reception jig is inserted between the duct wall of the large cylindrical portion and the flange portion, and pressure is applied to the porous member and the flange portion by a pressure jig and the reception jig so that the porous member is thermally welded with the flange portion.
According to the fourth aspect of the present invention, there is provided a hot plate welding method for welding first and second molded pieces by use of the a hot plate, which is applicable to manufacturing the air intake duct, the first molded piece being made of first resin, the second molded piece being made of second resin having a higher melting point than the first resin, the method comprising: bringing a joint surface of the second molded piece into contact with a surface of the hot plate heated to a temperature not lower than the melting point of the second resin so as to heat the joint surface of the second molded piece, while disposing the first molded piece in opposition to the other surface of the hot plate and away from the other surface so as to heat a joint surface of the first molded piece by radiation heat from the hot plate; and bringing the first and second molded pieces into pressure contact with each other in a condition that at least the joint surface of second molded piece is melted, so that the first and second molded pieces are welded with each other.
The first molded piece may be a cloth formed of fibers made of the first resin, and be impregnated with molten resin in the joint surface of the second molded piece so that the first and second molded pieces are welded with other.
In a hot plate welding method according to the present invention, the joint surface of a second molded piece having a high melting point is brought into contact with a hot plate heated to a temperature not lower than the melting point of the second molded piece, so as to be heated, in the same manner as that in the conventional case. Accordingly, the second molded piece can be melted and welded in the same manner as that in the conventional case. On the other hand, a first molded piece having a low melting point is disposed at a fixed distance from the hot plate so that the joint surface of the first molded piece is heated by radiation heat from the hot plate. The radiation heat becomes smaller as the distance between the hot plate and the first molded piece becomes larger. Accordingly, the heating state of the first molded piece can be controlled desirably by setting a desired distance between the first molded piece and the hot plate. Thus, the first molded piece can be heated to a temperature high enough to be welded but low enough to be prevented from deformation caused by softening. In this state, the hot plate is removed, and the first and second molded pieces are brought into pressure contact with each other and cooled. Thus, welding is completed.
Assume that the first molded piece is a cloth formed of fibers made of first resin having a low melting point. Then, the first molded piece is heated by the radiation heat from the hot plate so that the first molded piece can be heated to a temperature high enough to be impregnated with the molten resin of the melting joint surface of the second molded piece. Thus, the first molded piece can be welded with the first molded piece. In addition, the temperature of the first resin is low enough to prevent the joint surface of the first molded piece from melting. Thus, there is no fear that the first molded piece is softened and deformed. Accordingly, the first molded piece can be welded without damaging its air permeability. That is, when the second molded piece has a cylindrical shape with an opening, the first molded piece can be bonded with the opening to cover the opening. Thus, the opening can be covered while the air permeability of the first molded piece is ensured.
There is no special limit in the difference in melting point between the first and second resins. It will go well if the melting point of the second resin is higher than that of the first resin. In addition, as for the materials of the first and second resins, it will go well if both the resins are thermoplastic resins, and they are of materials capable of being welded with each other in the case where normal molded pieces are welded. Further, there is no special limit in the shapes of the first and second molded pieces.
The first molded piece may be a cloth formed of fibers made of first resin. Examples of such cloths include woven fabric, non-woven fabric, knitted fabric, and so on. The degree of air permeability of the first molded piece may be determined in accordance with the purpose. Of such cloths, non-woven fabric is preferably used because it is easy to manufacture. If the first molded piece is a cloth, a fibrous aggregate body, or the like, formed of fibers made of the first resin, the first resin does not have to be capable of being thermally welded with the second resin. If the fibers are impregnated with the molten second resin and the molten second resin is solidified among the fibers, the first and second molded pieces can be bonded by the anchor effect. This case is also included in xe2x80x9cweldingxe2x80x9d defined according to the present invention.
The distance between the joint surface of the first molded piece and the hot plate is determined in accordance with the temperature of the hot plate, the time of contact between the second molded piece and the hot plate, the melting point of the first resin, the atmospheric temperature, and so on. On the other hand, the heating time by radiation heat from the hot plate is determined in accordance with the temperature of the hot plate, the time of contact between the second molded piece and the hot plate, the distance between the first molded piece and the hot plate, the melting point of the first resin, the atmospheric temperature, and so on. Generally, the heating time becomes shorter if the distance is shorter, and the heating time becomes longer if the distance is longer.
Features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.